This invention is an improved endless conveyor belt that can be used to reorder or dry tobacco, or treat other particulate solid materials. The improvement comprises modification to a self-stacking spiral conveyor belt that traverses through a circulating treatment gas in the housing of a gas treatment apparatus. The modification allows treatment of much smaller-dimension discrete products than had been possible with open-web belts of the prior art. The modification also makes it possible to treat a packed bed of conveyed product rather than a single layer of relatively large discrete products. The invention also provides additional control over the gas flow within the gas treatment apparatus. These objectives are achieved without impairing the articulation of the belt links into the spiral. Prior art conveyor belts of this type are either self-stacking, i.e., the side links are in the form of side plates serving as spacers, the upper edge portions of which are adapted to engage the lower edge portions of the overlying turn of the conveyor belt so as to support this turn, or supported by separate rails following the spiral path of the conveyor belt.
A gas treatment apparatus in the form of a self-stacking spiral conveyor is known where products on the conveyor are treated by heat transfer from a treatment gas, such as refrigerating, freezing, or heating. The conditioning means for the treatment gas may be a heat exchanger which cools or heats the treatment gas before it circulates around and through the bed of conveyed product.
For example, a Frigoscandia self-stacking spiral conveying machine (e.g., a Model GCP 42 self-stacking spiral freezer supplied by Frigoscandia Food Process Systems AB of Helsingborg, Sweden) is disclosed in U.S. Pat. Nos. 3,938,651, 4,565,282, 4,603,776, 4,899,871, and No. 4,941,567. This apparatus, by virtue of its self-stacking spiral design and gas recirculation fans, channels the majority of gas flow downward through the multiple tiers of the conveyor, which are carrying the product.
Use of the appropriate treatment agent in the treatment gas permits a variety of non-thermal treatments to the conveyed product. The use of such a device for non-thermal treatments such as a process where air of controlled moisture content is used to increase the moisture content of tobacco is disclosed in copending, commonly-assigned U.S. patent applications Ser. Nos. 07/969,109 and 07/969,798, filed concurrently herewith and hereby incorporated by reference in their entireties.
The use of such a gas treatment apparatus has heretofore been limited by the open web of the conveyor belt to relatively large discrete solid objects such as hamburger patties. The prior art open-web belt used a series of interlocking flattened helical springs to prevent the conveyed material from falling through the gaps between the rods that supported the conveyor belt bottom. These rods and springs formed an open-web belt that was not adaptable for use with small or irregularly sized products such as cut tobacco leaves.
Additionally, the resistance to gas flow from the rods and springs was very low and essentially invariable. The fixed resistance to gas flow precluded varying the resistance to gas flow in the vertical direction as one tool to control the gas flow pattern within the conveyor stack.